-/* allocate at precisely the given address */
-void *rh_alloc_fixed(rh_info_t * info, void *start, int size, const char *owner)
+/* Allocate a block of memory at the given offset, rounded up to the default
+ * alignment. The value returned is an offset into the buffer initialized by
+ * rh_init(), or a negative number if there is an error.
+ */
+unsigned long rh_alloc_fixed(rh_info_t * info, unsigned long start, int size, const char *owner)